Long chain perfluoroalkyl iodides are prepared by the conventional telomerization of pentafluoroethyl iodide with tetrafluoroethylene (TFE). This telomerization yields perfluoroalkyl iodides with a polymer distribution of varying TFE insertions. Most current processes produce chain lengths from 8 carbons to 20 carbons in length. Perfluoroalkyl iodides have many uses as a key starting material in the preparation of surface modifying products, such as repellants, stain and soil resist agents, as well as surfactants. The current trend in these end use markets is the use of fluorine efficient molecules. Fluorine efficient molecules are those molecules that contain a shorter chain perfluoroalkyl component. To produce these fluorine efficient molecules, shorter chain perfluoroalkyl iodides are needed as starting materials.
Bertocchio et al., in U.S. Pat. No. 5,268,516, claims a process for preparation of shorter chain perfluoroalkyl iodides in a thermal telomerization of TFE with pentafluoroethyl iodide or heptafluoroisopropyl iodide by adjusting feed concentration and location of the TFE. This process is distinct in that it is a telomerization of TFE.
Becker et al., in German Patent Application DE 4,410,551A1, disclose a process for preparing short chain perfluoroalkyl iodides by reaction of longer chain perfluoroalkyl iodides (greater than 8 carbons in the perfluoroalkyl) with shorter chain perfluoroalkyl iodides (6 carbons or less in the perfluoroalkyl) to produce the desired short chain perfluoroalkyl iodides as well as inert perfluoroalkanes as a by-product. Becker et al., added iodine in the process to increase selectivity of the perfluoroalkyl iodide over the perfluoroalkanes, but it has been found that this also decreased the yield of the perfluoroalkyl iodides. The addition of iodine (I2) increases the presence of water into the system, potentially producing a second inert by product, hydro-end capped fluoroalkanes.
The use of iodine causes several issues in processes. Iodine introduces opportunities for line plugs, a need for iodine recycling and neutralization, and the potential hydrogen iodide formation. Iodine could also introduce water contamination into the process leading to production of unwanted inert by-products, hydro-end capped fluoroalkanes.
There is a need for a process for the production of shorter chain perfluoroalkyl iodides, that has high yields, high selectivity, and is free of the use of iodine as a reactant. The present invention meets these needs.